The x-ray tube has become essential in medical diagnostic imaging, medical therapy, and various medical testing and material analysis industries. Typical x-ray tubes are built with a rotating anode structure for the purpose of distributing the heat generated at the focal spot. The anode is rotated by an induction motor comprising a cylindrical rotor built into a cantilevered axle that supports the disc shaped anode target, and an iron stator structure with copper windings that surrounds the elongated neck of the x-ray tube that contains the rotor. The rotor of the rotating anode assembly being driven by the stator which surrounds the rotor of the anode assembly is at anodic potential while the stator is referenced electrically to ground. The x-ray tube cathode provides a focused electron beam which is accelerated across the anode-to-cathode vacuum gap and produces x-rays upon impact with the anode.
The casings of x-ray tubes are lined with lead to prevent the leakage of x-rays in directions other than through the window of the tube. This lead is exposed to a dielectric cooling oil which removes heat from the tube insert during operation. X-ray exposure causes a gradual breakdown in the oil forming smaller and less saturated compounds. The lead readily oxidizes and a combination of this oxide and particles on the lead surface make coating the lead necessary to prevent oil contamination.
Currently, various epoxy type paints are used to coat tube casings and prevent leakage of the x-rays. Unfortunately, the lead which lines the casings of x-ray tubes provides a poor surface for adherence. Hence, the hot oil, x-rays and chemicals generated during the x-ray exposure of the oil all gradually promote flaking of the paint from the surface. Furthermore, the enamel and epoxy paints currently used to coat tube casings are susceptible to peeling and scratching during assembly. The particles created by the flaking, peeling and scratching cause tube instability and tube failure. In addition, the casings often require manual touch-up of the paint, and paint damaged during handling and assembly creates rework requirements as well. All of these problems impact casing quality and availability and increase the casing cost.
It is seen, then, that it would be desirable to have a more adherent, durable and long-lasting coating for x-ray tube casings which can overcome the problems of prior art tube casing coatings.